The document discusses code optimization techniques and includes code snippets, control flow graphs, and syntax directed translation schemes. It asks to summarize various code optimization techniques and explain one in detail. Live variable analysis is discussed as well as determining the number of nodes and edges in a control flow graph and outputs of syntax directed translation schemes.

1. 1. Consider the following C code segment.
1.
for (i = 0, i<n; i++)
{
for (j=0; j<n; j++)
{
if (i%2)
{
x += (4*j + 5*i);
y += (7 + 4*j);
}
}
}
2.
c = a + b
d = c
c = c – e
a = d – e
b = b * e
b = d/b
3.
int i, j, x, y, m, n;
n=20;
for (i = 0, i < n; i++)
{
for (j = 0; j < n; j++)
{
if (i % 2)
{
x + = ((4*j) + 5*i);
y += (7 + 4*j);
}
}
}
m = x + y;
Optimize the above code using various code optimization techniques.
2. Consider the intermediate code given below:
1. i = 1
2. j = 1
3. t1 = 5 * i
4. t2 = t1 + j
5. t3 = 4 * t2
6. t4 = t3
7. a[t4] = –1
8. j = j + 1
9. if j <= 5 goto(3)
10. i = i + 1
11. if i < 5 goto(2)
The number of nodes and edges in the control-flow-graph constructed for the above code,
respectively, are __, ____. Justify it.
3. A variable x is said to be live at a statement si in a program if the following three
conditions hold simultaneously:

2. i. There exists a statement Sj that uses x
ii. There is a path from Si to Sj in the flow graph corresponding to the program
iii. The path has no intervening assignment to x including at Si and Sj
The variables which are live both at the statement in basic block 2 and at the statement in
basic block 3 of the above control flow graph are ?
4. Consider the following statements:
i. The output of a lexical analyser is groups of characters.
ii. Total number of tokens in printf("i=%d, &i=%x", i, &i); are 11.
iii. Symbol table can be implementation by using array and hash table but not tree.
Which of the following statement(s) is/are correct?
A. Only (I)
B. Only (II) and (III)
C. All (I), (II), and (III)
D. None of these
5. Which one of the following statements is FALSE?
A. Context-free grammar can be used to specify both lexical and syntax rules.
B. Type checking is done before parsing.
C. High-level language programs can be translated to different Intermediate
Representations.
D. Arguments to a function can be passed using the program stack.
6. A lexical analyser uses the following patterns to recognize three tokens T1, T2, and
T3 over the alphabet {a,b,c}. T1: a?(b∣c)*a T2: b?(a∣c)*b T3: c?(b∣a)*c Note that ‘x?’
means 0 or 1 occurrence of the symbol x. Note also that the analyser outputs the token
that matches the longest possible prefix. If the string bbaacabc is processes by the
analyser, which one of the following is the sequence of tokens it outputs?
A. T1T2T3
B. T1T1T3
C. T2T1T3
D. T3T3

3. 7. Consider the following Syntax Directed Translation Scheme (SDTS), with non-
terminals {S, A} and terminals {a,b}.
S → aA { print 1 }
S → a { print 2 }
A → Sb { print 3 }
Using the above SDTS, the output printed by a bottom-up parser, for the input aab is:
A. 1 3 2
B. 2 2 3
C. 2 3 1
D. syntax error
8. Consider the following translation scheme.
S → ER
R → *E {print("*");}R | ε
E → F + E {print("+");} | F
F → (S) | id {print(id.value);}
Here id is a token that represents an integer and id.value represents the corresponding
integer value. For an input '2 * 3 + 4', this translation scheme prints
A. 2 * 3 + 4
B. 2 * +3 4
C. 2 3 * 4 +
D. 2 3 4+*
9. Convert following program code into 3 address code.
1.
2.
3.

4. 10. For following source code, generate 3 address code, basic block and control flow graph.
11. Consider the grammar with the following translation rules and E as the start symbol.
E -> E1 #T {E.value = E1.value * T.value}

5. | T {E.value = T.value}
T -> T1 & F {T.value = T1.value + F.value}
|F {T.value= F.value}
F -> num {F.value = num.value}
Compute E.value for the root of the parse tree for the expression:2 # 3 & 5 # 6 &4.
A. 200
B. 180
C. 160
D. 40
12. List out code optimization techniques. Explain any one in detail.